. 2019 Jun 13;68(7):1366–1379. doi: 10.2337/db19-0119

Table 1.

Antigen-agnostic and antigen-specific candidate T-cell biomarkers for T1D

Specificity	Candidate biomarker	Observation	Assay	Cell number (PBMC)	Replicated		Proposed next steps	Reference
Specificity	Candidate biomarker	Observation	Assay	Cell number (PBMC)	Same laboratory	Independent laboratory	Proposed next steps	Reference
Antigen nonspecific (agnostic)	CD4 Tfh cell frequency	Increased frequency of memory Tfh in peripheral blood in at-risk progressors and new-onset and long-standing T1D. More Tfh in individuals with multiple autoantibodies. Definition of Tfh varies by study with regard to PD-1 and ICOS inclusion.	Flow cytometry	1–5 × 10⁶	Yes	Yes	Standardize definition of Tfh; biomarker validation	(10,65–68)
	CD4 Treg transcript signature	Expression of 37 gene transcript panel in purified, stimulated Tregs or PBMC distinguishes new-onset T1D, long-standing T1D, and T2D from healthy control subjects; predicts C-peptide decline over time.	Nanostring expression analysis	5–10 × 10³	Yes	Ongoing	Further biomarker validation in independent laboratory	(15)
	CD4 Teff resistance to suppression	Resistance of CD4 Teff (CD4⁺CD25⁻) from established T1D to Treg suppression compared with Teff from healthy control subjects.	Flow cytometry	2 × 10⁷	Yes	Yes	Replication of shorter assay in independent laboratory; biomarker validation	(69–71)
	FOXP3⁺IFN-γ⁺ Tregs	Increased frequency of Helios⁻ FOXP3⁺IFNγ⁺ adaptive Tregs in T1D compared with healthy control subjects.	Flow cytometry	1–5 × 10⁶	Yes	Yes	Biomarker validation	(72,73)
	CD4 T-cell IL-2 response	Decreased IL-2 pSTAT5 signaling in CD4 Treg and CD25⁺ and CD25⁻ memory T cells compared with healthy control subjects. Impacted by genotype at IL2RA and PTPN2 genes. Results in reduced FOXP3 stability and reduced frequency of memory and activated Tregs in high vs. low IL-2 T1D responders.	Flow cytometry	5 × 10⁶	Yes; technically reproducible and stable over time	Yes	Biomarker validation	(12–14)
	IL-17⁺ T-cell frequency	Increased frequency of CD4 naive or memory T cells and CD8 T cells that are IL-17⁺ upon stimulation in recent-onset and long-standing T1D. Impacted by IL2RA genotype in at-risk subjects.	Flow cytometry, ELISA, PCR	1 × 10⁷	Yes	Yes	Standardization of assay; biomarker validation	(68,74–76)
Antigen specific	Islet-specific CD8 T-cell frequency	Increased frequency of class I islet Mmr⁺ CD8 T cells in peripheral blood or pancreas in recent-onset or established T1D compared with healthy control subjects. Increased frequency of islet Mmr⁺ CD8 T cells associated with recurrent autoimmunity following islet transplant.	Class I multimers	1–5 × 10⁶	Yes	Yes	Clinical validation; expansion to include additional HLA types	(3,16,18,19)
	Islet-specific CD4 T-cell frequency and phenotype	Increased frequency of islet-specific CD4 T cells to classic or posttranslationally modified islet epitopes in peripheral blood in recent-onset or established T1D compared with healthy control subjects. Higher frequency of islet CD4 T cells associated with shorter disease duration. Islet CD4 T cells with an effector memory phenotype correlated with insulin antibody titer.	Class II tetramers, antigen-stimulated proliferation	5–10 × 10⁶	Yes	Yes; proliferation assays not rigorously tested in multiple laboratories	Standardization of assay; clinical validation; prioritization of available epitopes; expansion to include additional HLA types	(20–26,49,77–79)
	Inflammatory islet-specific T-cell signature	Increased frequency of IFN-γ⁺ islet antigen-stimulated T cells in new-onset and established T1D compared with healthy control subjects that had IL-10⁺ T-cell response. Reduction in IFN-γ⁺ T cells in new-onset T1D during the first year post-diagnosis. Higher frequency IFN-γ⁺ T cells in children than adults. IFN-γ⁺ islet antigen specificities differed in children vs. adults and with disease duration.	ELISpot	2 × 10⁷	Yes	Yes	Optimize for use with cryopreserved cells; standardize assay; clinical validation	(5,28–33,49)

All biomarkers listed have been tested in stage 3 T1D. Teff, effector T cells; T2D, type 2 diabetes; pSTAT5, phosphorylated STAT5; Mmr, multimer; ND, not determined.